By: Kurt G. Briscoe
July 2002

On May 28, 2002, the United States Supreme Court in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. (hereinafter “the Supreme Court’s Festo decision”) handed down a very significant decision clarifying the application of the doctrine of equivalents. The doctrine of equivalents is an extremely important doctrine of United States patent law, which in certain cases extends the scope of the protection afforded by a patent claim beyond its literal wording.

The Supreme Court’s Festo decision upheld the Federal Circuit’s holding that extended the doctrine of prosecution history estoppel to include any narrowing amendment made for “a reason substantially related to patentability.” Under the doctrine of prosecution history estoppel, the range of equivalents accorded to a patent claim cannot be so broad as to cover subject matter “surrendered” by the patentee during prosecution. Historically, subject matter has been considered “surrendered” only in response to prior art rejections.

The Supreme Court, however, reversed the Federal Circuit’s holding that a finding of prosecution history estoppel acts as a “complete bar” to the application of the doctrine of equivalents as to any patent claim element that has been narrowed. If a “complete bar” applied, then no range of equivalents would have been available for any claim element narrowed. The Supreme Court maintained the “flexible bar” approach as to narrowed claim elements, but conditioned its application upon a showing by the patentee that the allegedly equivalent element could not have been literally embraced by the appropriate choice of claim language during patent prosecution. This showing is likely to constitute a difficult burden for the patentee to discharge.

In view of these developments in the law, we recommend that prior art searches be conducted prior to the filing of a patent application, and that original patent application claims be drafted in view of the prior art uncovered, to reduce the need for narrowing amendments to be made during patent prosecution. Further, if a narrowing amendment must be made, a determination should be made as to what subject matter might be considered to be surrendered by the amendment so that the potential scope of protection under the doctrine of equivalents can be ascertained.